Natural boundaries are an important component of physical-geographical regionalization. They exist objectively within the physical-geographical cpmplex and allow a differentiation in the terrain in a visual way. Two boundaries were identified in the area between Hanoi and Da Nang which delineate three physical-geographical regions. These boundaries are (i) the Tam Diep mountains, a natural boundary separating NorthlNortheast Vietnam from Northwest/North Central Vietnam, (ii) the Bach Ma mountains. the natural boundary that separates Northwest/North Central Vietnam from South Central/South Vietnam. the authors also identified natural boundaries \
Vithin the physical-geographical zones: the Red River delta and the Thanh Nghe Tinh plains. the Thanh Nghe Tinh plains and the Binh Tri Thien plains, the Binh Tri Thien plains and the coastal plains of South Central Vietnam and the North Truong Son and the South Truong Son Mountains.